Tucson is a city in and the county seat of Pima County, Arizona, United States, and is home to the University of Arizona. It is the second-largest city in Arizona behind Phoenix, with a population of 542,629 in the 2020 United States census, while the population of the entire Tucson metropolitan statistical area (MSA) is 1,043,433. The Tucson MSA forms part of the larger Tucson-Nogales combined statistical area. Both Tucson and Phoenix anchor the Arizona Sun Corridor. The city is 108 miles (174 km) southeast of Phoenix and 60 mi (100 km) north of the United States–Mexico border.

Pima County is a county in the south central region of the U.S. state of Arizona. As of the 2020 census, the population was 1,043,433, making it Arizona's second-most populous county. The county seat is Tucson, where most of the population is centered. The county is named after the Pima Native Americans, also known as Tohono O'odham, who are indigenous to this area.